Edema

• Excess fluid in the tissuesIntracellular EdemaExtracellular Edema

Intracellular Edema 1) Hyponatremia(2) Depression of the metabolic systems of the tissues(3) Lack of adequate nutrition to the cells 4) Intracellular edema can also occur in inflamed tissues. Inflammation usually increases cell membrane permeability

Extracellular Edema

• Excess fluid accumulation in the extracellular spaces

abnormal leakage of fluid from the plasma to the interstitial spaces across the capillaries

failure of the lymphatics to return fluid from the interstitium back into the blood called lymphedema

Capillary Filtration

Factors That Can Increase Capillary Filtration

• Increased capillary filtration coefficient • Increased capillary hydrostatic pressure.• Decreased plasma colloid osmotic pressure

I. Increased capillary pressure I. Excessive kidney retention of salt and water

I. Acute or chronic kidney failure II. Mineralocorticoid excess

II. High venous pressure and venous constriction I. Heart failure II. Venous obstruction III.Failure of venous pumps

(a) Paralysis of muscles (b) Immobilization of parts of the body (c) Failure of venous valves

III.Decreased arteriolar resistance I. Excessive body heat II. Insufficiency of sympathetic nervous system III.Vasodilator drugs

I. Decreased plasma proteins a. Loss of proteins in urine (nephrotic syndrome) b. Loss of protein from denuded skin areas

I. Burns II.Wounds

c. Failure to produce proteins III.Liver disease (e.g., cirrhosis) IV.Serious protein or caloric malnutrition

I. Increased capillary permeability I. Immune reactions that cause release of histamine

and other immune products II.Toxins III.Bacterial infections IV.Vitamin deficiency, especially vitamin C V.Prolonged ischemia VI.Burns

I. Blockage of lymph return I. Cancer II.Infections (e.g., filaria nematodes) III.Surgery IV.Congenital absence or abnormality of lymphatic

vessels

Safety Factors That Normally Prevent Edema

(1) low compliance of the interstitium when interstitial fluid pressure is in the negative pressure range

(2) the ability of lymph flow to increase 10- to 50-fold (3) washdown of interstitial fluid protein concentration which reduces interstitial fluid colloid osmotic pressure

1.The safety factor caused by low tissue compliance in the negative pressure range is about 3 mm Hg.

2.The safety factor caused by increased lymph flow is about 7 mm Hg.

3.The safety factor caused by washdown of proteins from the interstitial spaces is about 7 mm Hg

• The total safety factor against edema is about 17 mm Hg

• This means that the capillary pressure in a peripheral tissue could theoretically rise by 17 mm Hg before marked edema would occur